OBJECTIVE To determine pregnancy outcome, including the rate of repeat molar pregnancy, following histologically confirmed complete or partial hydatidiform mole. METHODS Retrospective review of a large supraregional database of registrations for gestational trophoblastic disease. METHODS Supraregional Trophoblastic Disease Unit, London. METHODS Women with pregnancies affected by complete or partial hydatidiform mole registered between 1992 and 1998. METHODS All patients with a diagnosis of histologically confirmed complete or partial hydatidiform mole were identified and data on subsequent pregnancies compared between groups using comparison of proportion test. METHODS Pregnancy outcome by partial or complete mole subtype, with particular regard to risk of subsequent molar pregnancy. RESULTS Of 2578 complete moles, the subsequent pregnancy was affected by hydatidiform mole in 27 (1.9%) cases, including 22 (81%) complete moles and 5 (19%) partial moles. Of 2627 partial moles, the subsequent pregnancy was also molar in 25 (1.7%) cases, including 17 (68%) partial moles and 8 (32%) complete moles. Overall recurrence risk for molar pregnancy was 1.8% (1 in 55), or a 20-fold increase compared with the background risk. Of 27 cases with repeat complete moles, three had further complete moles, suggesting the recurrence risk following two previous complete moles is approximately 10%. There were no other significant differences in pregnancy outcome between cases with previous complete or partial hydatidiform mole and that expected in an unselected obstetric population. CONCLUSIONS Women having a pregnancy affected by a histologically confirmed complete or partial hydatidiform mole may be counselled that the risk of repeat mole in a subsequent pregnancy is about 1 in 60 and if this were to occur, the majority of cases will be of the same type of mole as the preceding pregnancy. However, >98% of women who become pregnant following a molar conception will not have a further hydatidiform mole and these pregnancies are at no increased risk of other obstetric complications.